George Galloway has said he is confident a judge will hear his legal challenge against the Batley and Spen by-election result, despite the initial deadline for challenging his defeat having passed.

Former MP Mr Galloway, who lost to Labour’s Kim Leadbeater in the poll on July 1, said he had “multiple grounds” to overturn the result after the outcome was announced, and his campaign manager James Giles promised “the mother of all court cases”.

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Those wishing to challenge an election must do so through the Election Petitions Office within 21 days.

Batley and Spen by-electionNewly elected Labour MP for Batley and Spen Kim Leadbeater is welcomed to the House of Commons by party leader Sir Keir Starmer (Stefan Rousseau/PA)

In some cases, a judge may allow a challenge after this period but only if there were “corrupt or illegal practices, for example bribery” or if the complaint involves election expenses.

But the Local Democracy Reporting Service previously reported that the most significant aspect of the complaint was that Mr Galloway’s campaign was damaged when Ms Leadbeater was verbally attacked for supporting LGBT rights outside a mosque.

In a subsequent interview, Ms Leadbeater claimed Mr Galloway had laughed at her while she was being shouted at, but Mr Galloway denied this.

Another area involved a decision by Kirklees Council to remove Mr Galloway’s campaign posters because information on who had printed the material, the promoter and the candidate was found to be 50% too small.

Neither of these issues appeared to fall under the remit for a challenge after the first 21 days, and the Election Petitions Office confirmed to the PA news agency that it had not yet received any complaint.

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However, the Workers Party candidate Mr Galloway told PA the challenge was with lawyers and added: “We have been working hard to compile a serious case of multiple breaches of the law by the Labour campaign and are confident the judge will hear it.”

A Labour source said: “There continues to be an enormous gulf between Mr Galloway’s fanciful claims and reality. He’s little more than a purveyor of low-grade fertiliser.”

In 2015, Mr Galloway said he would bring a challenge over the result in Bradford West, where he lost his seat to Labour’s Naz Shah by more than 11,000 votes.

But on that occasion, the deadline also expired before a complaint was made.

In a UK parliamentary election, results can be challenged, via an election petition, by anyone who has the right to vote in it, or by a candidate.

It costs £528 to issue a petition, along with a deposit of up to £5,000 against future legal bills, known as security for costs.

A fee of £100 must also be paid to apply for the security of costs.

Mr Galloway’s decision to stand in the Batley and Spen by-election, which was prompted by former Labour MP Tracy Brabin becoming West Yorkshire mayor, was seen as a serious threat to Labour but the race was mired in intimidation claims.

He ended up in third place behind Labour and the Tories.

Ms Leadbeater squeezed home by only 323 votes after a bitter and divisive campaign that many had predicted the party would lose.

The result came as a huge relief to Labour leader Sir Keir Starmer after the party’s damaging loss in the Hartlepool by-election in May.